The four critical updates -- the highest threat ranking in Microsoft's four-step system -- will patch 13 bugs, including an unknown number in Windows Server 2012, Windows 8 and Windows RT, the operating system that powers Microsoft's own Surface RT tablet, according to the advance warning Microsoft published Thursday.

The Windows 8 and Windows RT security updates will be the first shipped since those operating systems' launch on Oct. 26. While Microsoft had previously issued patches for the new OSes, all but a September "out-of-band" fix for IE tackled problems in its unfinished previews, not the final code.

But Andrew Storms, director of security operations at nCircle Security, downplayed the patches for Windows 8 and Windows RT.

"I'd be more worried if they didn't patch them right off the bat," said Storms. "They've had them in development so long, someone should have found a bug by now. And it shouldn't be surprising.... We all know that everything has bugs, even the newest software."

Another researcher agreed. "This may come as a surprise to many who expected that Windows 8 [would] be much more secure than legacy versions," said Marcus Carey of Rapid7 in an email. "The truth is that Microsoft and other vendors have significant technical debt in their code base which results in security issues."

The update slated for IE is among the critical quartet, and will address one or more vulnerabilities in IE9, now the second-newest browser in Microsoft's stable. IE9 runs only on Windows 7 and Windows Vista.

IE6, IE7 and IE8 -- all which run on the 11-year-old Windows XP -- will not be patched; nor will IE10, the just-released browser bundled with Windows 8 and Windows RT.

"What did they add in IE9 that wasn't in the earlier versions?" Storms asked. "What went wrong?"

Although Storms held off predicting that the IE9 update will be the one to patch first next week -- he said he was concerned about Bulletin 4, which will address unknown bugs in the .Net development framework -- Carey was not hesitant to call a winner in that dubious sweepstakes.

"This will be the top priority for both businesses and consumers since an attacker would be able to compromise their system if the user visits a malicious Web page," Carey said.

According to Carey, the IE9 bug can be used in "drive-by" exploits, those that only require a user be tricked into browsing to an unsafe website.

Web metrics company Net Applications has estimated that IE9 accounted for about 38% of all versions of IE used last month, second only to IE8, which owned a 45% share of the Microsoft browser base.

Next week's IE update will be the first since Microsoft delivered a rush patch to stymie active attacks exploiting a bug. The Sept. 21 out-of-band update, which also included fixes for several other vulnerabilities, had been originally slated to ship two weeks later.

Another update, pegged "moderate" by Microsoft, will patch four flaws in Office's Excel spreadsheet. All still-supported versions of the suite -- ranging from Office 2003 to Office 2010 on Windows, and Office 2008 and Office 2011 on OS X -- will receive the update.

And Storms wondered what Microsoft would reveal next week about Bulletin 4, today's label for an update to the .Net framework within all versions of Windows. Windows RT's Bulletin 4 patch was rated "important," but fixes for all other versions, including Windows 8 and Server 2012, were pegged critical.

"Bulletin 4 could take the cake next week," said Storms. ".Net is so ubiquitous, used not only in software but also in Web services. And who knows where the bug is?"

Microsoft will release the six updates at approximately 1 p.m. ET on Nov. 13.